Early last year, we built a a breadboard with a Teensy microcontroller (instead of an Arduino) to decode signals from off-the-shelf door and window sensors. At the time, we had to reverse engineer the protocol using a oscilloscope. :) The breadboard was tethered to an Android device, which was the brain of the system (and this let us do other cool stuff, like video, networking etc).

We're much further along now (with working prototype units). If you're interesting in this kind of thing, we ARE hiring. :) (http://elarm.com)

They cost significantly more (about as much as a decent PC) but I would not trust my property or life to anything less honestly. My Omni has been running without reboot for years and does security/fire/hvac/irrigation/lighting/garage door control and has an iPhone app for control.

It is, however, vulnerable to the outrageous latency problems (minutes, often) the unofficial messaging gateways have. I send my wife texts to her company blackberry because it's convenient, but ultimately had to duplicate them to her gmail address to ensure that she got them fast enough.

Nice job aimatt. Good learning project.

The cheapest way to solve the issue would be to hook it up to something like a nokia pay as you go phone over serial/bluetooth.

All the ones I have used were expensive industrial spec units with complex data channels.

Has serial port which takes AT commands. Easy enough to drive it.

Costs $20 a shot.

I have tried out. Well documented and you can get the breakout boards for $5 but I forget precisely where. Managed to get it working in UK on O2 pay as you go. Now in junk box :(

Watch out - you need a level shifter if you're using an Arduino or something as it has 3v3 operation. I used an old(er than me) HP lab PSU and a crudely hacked up set of BC548 switches as a level shifter. You need an antenna and a sim socket (my sim was cruely soldered onto 1/0.2 solid wire and plugged into the breakout board header).

OR you can buy this arduino shield: http://www.sparkfun.com/products/9607 $100

tl;dr Limor Fried is a bad ass, buy things from her store.

I pay about half the price of what I see in most web stores.

- What's the cheapest Arduino board that would work with this sensor? Wouldn't it be cheaper to get a Raspberry Pi?

- How much is the power supply?

- It would also be cool if there was a way to send SMS over the regular wireless, like with one of those cheap emergency cell phone plans. That would make it a really nice alarm, no need for the internet, and it can work off a PSU even if burglars shut down the power/internet.

2. Do you really want to try and optimize for cost on sub 30 dollar items in quantities of approximately 1?

3. ADH8066 GSM Modules are approximately fifty bucks. Serial port, AT commands, etc. Who knows where you can get a data carrier for reasonable cost in this country.

I would love to see this on a Raspberry Pi, but you will likely have to do some 3v3 to 5v translation or use the upcoming Gertboard.